U.S. patent number 4,603,422 [Application Number 06/654,355] was granted by the patent office on 1986-07-29 for long-lived laser dye.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Aaron N. Fletcher.
United States Patent |
4,603,422 |
Fletcher |
July 29, 1986 |
Long-lived laser dye
Abstract
A method of obtaining a long-lived flashpumped laser dye with an
output equivalent to commercial dyes and a low threshold of lasing
using the N-methyl tosylate salt of
2-(4-pyridyl)-5-(4-methoxyphenyl) oxazole.
Inventors: |
Fletcher; Aaron N. (Ridgecrest,
CA) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
24624527 |
Appl.
No.: |
06/654,355 |
Filed: |
September 26, 1984 |
Current U.S.
Class: |
372/53;
252/301.16; 252/301.17; 372/54; 546/271.4 |
Current CPC
Class: |
H01S
3/213 (20130101) |
Current International
Class: |
H01S
3/14 (20060101); H01S 3/213 (20060101); H01S
003/20 () |
Field of
Search: |
;372/53
;260/296R,296,37R ;252/301.16,301.17 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Fletcher et al., "Fluorescence and Lasing Charact. of Some
Long-Lived Flaamp-Pumpable, Oxazole Dyes"; Opt. Comm., 48(5), p.
352, (1984)..
|
Primary Examiner: Scott, Jr.; Leon
Attorney, Agent or Firm: Beers; R. F. Skeer; W. T.
Claims
What is claimed is:
1. A method of obtaining in a flashlamp pumped laser system, a
long-lived flashpumped laser dye having a low threshold of lasing
and a moderate output comprising the steps of:
placing a dye solution comprising a laser dye, the N-methyl
tosylate salt of 2-(4-pyridyl)-5-(4-methoxyphenyl)oxazole, having
the structure: ##STR2## and a solvent into a laser dye cavity;
screening said dye solution from ultraviolet light with an optical
filter;
flushing said dye solution with an inert gas; and
optically pumping said dye solution with a flashlamp to produce
laser emission.
2. The method of claim 1 wherein said solvent is selected from the
group consisting of ethanol and methanol.
3. The method of claim 1 wherein said inert gas is argon.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of chemistry. More
particularly, this invention relates to dye lasers. Still more
particularly, but without limitation thereto, this invention
relates to a method of obtaining a long-lived flashpumped laser dye
with an output equivalent to commercial dyes and with a low
threshold of lasing.
2. Description of the Prior Art
The class and wavelength of laser dyes of interest are in the range
of 560 to 585 nm. More specifically, the desirable lasing
wavelength is 560. This particular wavelength region has rhodamine
dyes (strongest output) that lase, yet they have lower lifetimes.
Other dyes in this region include brilliant sulfaflavine, fluoral
555 (both with low outputs) and shifted coumarin dyes.
Research has been done with oxazoles yet they have shown little
success as flashlamp-pumpable laser dyes. Considerable improvement
was shown when molecular engineering was performed on the oxazoles
to make them more absorptive and to attach triplet-state quenchers
to them. However, the lasing outputs of the modified oxazoles were
still low compared to other classes of dyes.
Salts of a pyridyl substituted phenyloxazole in water have
exhibited relatively low laser outputs and moderate durations of
lasing with flashlamp pumping. The effects of dye structure, cover
gas and solvent are all critical to laser output and lifetime. This
invention establishes that under very specific experimental
conditions, one of the oxazole dye modifications yields the highest
lifetime with moderate laser output of any laser dye solution
reported. See A. N. Fletcher, R. A. Henry, R. F. Kubin and R. A.
Hollins, Fluorescence and Lasing Characteristics of Some Long-Lived
Flashlamp-Pumpable, Oxazole Dyes, Optics Com. 48, pp. 352-356
(1984).
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for
obtaining a long-lived moderate output laser dye.
A further object of the present invention is to provide a method of
obtaining in a flashlamp pumped laser system, a long-lived
flashpumped laser dye having a low threshold of lasing and a
moderate output.
These and other objects have been demonstrated by the present
invention wherein the dye solution comprised of an oxazole laser
dye and a solvent are placed in a laser dye cavity, screened from
ultraviolet light by a glass filter, and then flushed with an inert
gas. The dye solution is then pumped with a flashlamp to produce
laser emission.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The test setup uses a triaxial flashlamp having a 300 nm cutoff
ultraviolet filter to contain the lasing solution (laser cavity)
separating it from the water coolant. The rise time of the triaxial
flashlamp used is 200 ns. The output mirror has a nominal 55%
reflectivity at the lasing wavelength.
Additionally, a wavelength and intensity corrected linear flashlamp
for dye degradation is used. The linear flashlamp is water cooled
and operates at 10 J (electrical) input. A portion of this setup is
made of optical glass to serve as a wavelength filter. In
developmental models of the invention, this filter was made of a
glass known as "Pyrex" a trade name of the Corning Glass Works of
Corning, New York. The glass of other manufacturers may be
substituted as dictated by good engineering practice.
The concentrations of the solutions used for flashlamp testing are
selected so as to have an absorbance of 4 to 5 cm.sup.-1 in the
S.sub.0 .fwdarw.S.sub.1 absorption band.
Laser outputs .PHI., for a specific electrical input energy to the
flashlamp I, are computer fitted to the relationship derived in
Fletcher et al., Applied Physics B29, p. 139 (1977),
where T is the total input energy .SIGMA.I, per unit volume. The
initial lasing slope efficiency k.sub.o, is taken as equivalent to
b, while the initial lasing threshold t.sub.o, is taken as
equivalent to -a/k.sub.o. The lifetime constants should be taken as
relative measurements since there has not yet been any demonstrated
capability to transfer such constants between different laser
configurations.
Several modifications of oxazole dyes were studied. The dye
modification showing the greatest improvement is the attachment of
a methoxy to a phenyl group to yield the N-methyl tosylate salt of
2-(4-pyridyl)-5-(4-methoxyphenyl)oxazole (hereinafter 4PyMPO-MePTS)
having the following structure: ##STR1##
This group causes a very marked red-shift in fluorescence and
lasing wavelengths. The fluorescence characteristics of
4PyMPO-MePTS are shown in Table 1.
TABLE 1 ______________________________________ Fluorescence
Measurements of 4PyMPO-MePTS Emission Fluorescence quantum yield
under Solvent peak, nm Argon Air Oxygen
______________________________________ ethanol 567 0.76 0.73 0.65
water 578 0.35 0.38 0.37 ______________________________________
It is surprising that 4PyMPO-MePTS can be made to lase at all in
water since it has a fluorescence quantum yield of only 0.38. The
results of attempts to lase 4PyMPO-MePTS under air in ethanol show
a very high threshold even though oxygen shows little effect upon
the fluorescence. Thus, attempts to lase this dye in water or
ethanol under air using flashlamp pumping would suggest a very poor
dye.
However, when dissolved in ethanol under argon, 4PyMPO-MePTS is the
longest-lived, moderate output dye of the laser dyes studied.
Several tests were done with 4PyMPO-MePTS in various solvents and
the results are presented in Table 2.
TABLE 2
__________________________________________________________________________
Flashlamp-Pumped Lasing Characteristics of 4PyMPO-MePTS Lasing
Slope Lifetime Concentration, Cover Efficiency, Threshold,
constant, Wavelength, molar Solvent Gas k.sub.o .times. 10.sup.3
t.sub.o, J l/c, MJdm.sup.-3 nm
__________________________________________________________________________
2 .times. 10.sup.-4 ethanol air .sup. n.d..sup.1 -50.0 n.d. n.d. 1
.times. 10.sup.-4 ethanol argon 1.6 21.0 2,000.0 560-583 2 .times.
10.sup.-4 ethanol argon 1.5 22.0 >10,000.0 567-587 1 .times.
10.sup.-4 2-propanol air n.d. -45.0 n.d. n.d. 1 .times. 10.sup.-4
2-propanol argon 1.4 16.9 16.0 559-582 2 .times. 10.sup.-4 methanol
argon 1.0 25.6 >10,000.0 571-588 2 .times. 10.sup.-4 water argon
0.45 41.0 n.d. 571-591
__________________________________________________________________________
.sup.1 not determined
Only at 1.times.10.sup.-4 molar was a lifetime measured for the dye
in ethanol. Going to 2.times.10.sup.-4 M and using 600 ml of
solution, the lasing output slightly increases after 50 hours of
testing a continuous electrical input of 250 W. Thus the dye was
too stable to be able to determine its lifetime constant within 50
hours.
A similar high lifetime is observed using methanol under argon but
with reduced laser output. In 2-propanol, however, the lifetime of
4PyMPO-MePTS is only moderately good. Again, oxygen causes a marked
quenching of the lasing output in both of these last two
solvents.
This invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *